Resonant ultrasound spectroscopy (RUS) is a non-destructive testing method where a manufactured component is subjected to exciting vibrations over a selected frequency spectrum and the resonant responses of the component are detected over the spectrum. Considerable information can be obtained from the distribution of the resonant responses in the spectrum. For example, U.S. Pat. No. 5,062,296, issued Nov. 5, 1991, teaches a method for deriving a characteristic signature of a component, where the signature can be used as an acceptance/rejection criteria. U.S. Pat. No. 5,351,543, issued Oct. 4, 1994, teaches a method for crack detection by comparing RUS spectra in dry and wet conditions. U.S. Pat. No. 5,355,731, issued Oct. 18, 1994, teaches the use of RUS to determine the sphericity of a component.
A significant problem occurs during the data acquisition phase of non-destructive testing using RUS when the driving frequency of the exciting transducer is changed. When a component being tested is vibrated near a natural resonant frequency, the amplitude of the induced vibration decays slowly, i.e., rings, after the driving vibration is removed. If a new exciting vibration frequency is applied while the component is still ringing from a previous exciting frequency, the component requires time to equilibrate to the new frequency. For some period of time there is an interference between the ringing frequency and the applied frequency so that accurate data is not available during that period of time.
Thus, data cannot be collected more rapidly than the ringing permits and the overall speed of the RUS system degrades rapidly near a component resonance. The time period between data collection points is referred to herein as the "dwell" time, or simply "dwell." FIGS. 1A and 1B illustrate the effect of dwell on the collected data. FIG. 1A depicts data taken with a relatively small dwell time (1 ms). The ringing is clearly seen as a succession of oscillations at slightly higher frequencies than the peak frequency. FIG. 1B depicts data taken with a longer dwell time (40 ms) and there is no apparent ringing.
As the amount of dwell is increased, the total time required to collect the necessary data is increased. Consider a set of data such as shown in FIG. 1B. Here, 400 data points were acquired for the single scan. With a dwell of 40 ms for each data point, a total dwell time of 16 seconds (400 points.times.40 ms/point) is required for the scan. This is time the system is simply waiting for the component to come to equilibrium.
The present invention recognizes that only about 70 of the 400 data points are near the resonance. A long dwell is required only for these 70 data points. Thus, if a dwell of 1 ms is used for all but these points, the total time required to collect the data is reduced to only 3.13 seconds (70 points.times.40 ms/point+330 data points.times.1 ms/point), for a time savings of 12.87 seconds for each scan.
Thus, it is an object of the present invention to minimize the time required for RUS scans of components being tested.
Yet another object of the present invention is to adaptively adjust the dwell for data acquisition.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.